[WolfeMacleod]

My GF recently bought a 1997 Dodge Dakota 4x4 with the 5.2 litre V8. Nice truck, well taken care of, but there's a nagging issue.

Oil pressure.

We figured it could be a bad oil pressure sending unit, so it's been replaced. Twice, actually. She took it into her mechanic to get checked over, brakes, etc. He replaced the sending unit we put in! She was told he'd hooked up a manual reader, and pressure was reading fine...
But still, when the engine is warm and at idle, the truck starts dinging away with oil pressure warnings and the gauge drops to zero. Oil pressure seems fine when it's cold. No knocking or anything though. It drives fine with no unusual noises.

Is this a normal thing for these trucks?

We're currently running some Seafoam in the crank case, hoping it might dislodge some sludge or something.

She also has a 99 Dakota with the V6. This doesn't happen with that truck, pressure is always right around the higher middle range of the gauge.